There has been known an optical transmission device that includes an erbium-doped fiber amplifier (EDFA) and a variable optical attenuator (VOA) so as to meet the needs of producing a high output and having a high optical signal-to-noise ratio (OSNR). This optical transmission device performs previous adjustment to find a monitored value of the optical output corresponding to optical output power of a target value. First, the VOA is controlled, whereby feed-forward control (FF control) is performed on a VOA digital-analog converter (DAC) so that a target optical output can be attained. The EDFA is then controlled, whereby feed-back control (FB control) is performed on an EDFA DAC, which drives an excitation light source for the EDFA, so that the monitored optical output value can attain a target value. An optical transmission device is thus started up.
Related conventional techniques include Japanese Laid-open Patent Publication No. 2008-300812 and Japanese Laid-open Patent Publication No. 06-45682.
A conventional optical transmission device, however, performs FB control on an EDFA after the FF control on a VOA is converged. The convergence of the FB control takes an undesirable length of time because FB control uses a gain such that optical output does not overshoot. As a result, starting up the optical transmission device takes an undesirable length of time.